Evaporator for looped heat pipe system and method of manufacturing the same

ABSTRACT

An evaporator for a looped heat pipe (LHP) system, in which a working fluid circulates to cool a heat generating electronic component that generates heat during operation, the evaporator including: a body including an inlet through which the working fluid enters and an outlet through which the working fluid is discharged; a sintered wick that is included in the body, wherein the sintered wick is formed by sintering a copper powder, and a plurality of pores are formed in the sintered wick; and an additional layer that is formed on a surface of the sintered wick, wherein the additional layer is formed by sintering copper particles having a size smaller than that of the copper powder forming the sintered wick, and the working fluid moved from the sintered wick is changed in a vapor state to be discharged.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No.10-2012-0134877, filed on Nov. 26, 2012, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an evaporator that forms a looped heatpipe system with a condenser, a vapor transport line, and a liquidtransport line, and a method of manufacturing the evaporator, and moreparticularly, to an evaporator for a looped heat pipe system, includingan additional layer, which is formed by sintering nano-sized particleson an vaporization surface of a sintered wick inside the evaporator, andthus having improved cooling efficiency.

2. Description of the Related Art

Electronic components such as a central processing unit (CPU) or asemiconductor chip, used in various electronic devices such as computersor servers generate a lot of heat during operation. The electroniccomponents are designed to perform their functions usually at roomtemperature, and thus if the heat generated during operation is noteffectively dissipated, not only is performance of the electroniccomponents degraded but the electronic devices are damaged in somecircumstances.

As electronic products are reduced in size to be slim, installationintervals between electronic components thereof that generate heatduring operation are continuously reduced, and thus, currently, the heatgenerated during use of the electronic products is not properlydissipated. Also, due to the high integration degree and highperformance of the electronic components, a heat generation load of theelectronic components is continuously increasing, and thus it isdifficult to cool the electronic components using conventional coolingmethods.

As a new technology for solving this problem, a phase change heattransport system capable of cooling electronic components having ahighly thermal density has been introduced.

One example of the phase change heat transport system is a cylindricalheat pipe. As illustrated in FIG. 1, a typical cylindrical heat pipe 100is used to perform cooling as a working fluid is circulated using acapillary pumping force of a sintered wick 102 installed on an innerwall of the cylindrical heat pipe 100.

Upon receiving heat from a heat source 101, the working fluid containedin the sintered wick 102 is evaporated and is transferred along an arrow103 denoting a vapor flow, and then heat of the working fluid is takenaway by a heat sink 104, and the working fluid is condensed again andflows through the sintered wick 102 along an arrow 105 denoting a liquidflow, by a capillary pumping force, to thereby circulate.

However, although dependence of a heat pipe on a gravity field is low,there are still limitations regarding arrangement of components; forexample, if a condensation section is located below an evaporationsection in a gravity field, heat transport capability of the heat pipedecreases greatly. Thus, if the heat pipe is applied as a cooling systemin an electronic product, the heat pipe may be a restriction on astructure of the electronic product.

In addition, since a vapor and a liquid flow in opposite directions in astraight cylindrical heat pipe, the vapor and the liquid mix in a middleportion of the pipe. Through the mixture, an amount of heat to betransferred is substantially reduced compared to a heat amount that canbe transferred theoretically.

A looped heat pipe (LHP) system is suggested as an ideal heat transfersystem to solve the problems due to the structure restriction and themixing of a vapor and a liquid.

An LHP system is a type of capillary pumped loop heat pipe (CPL)developed by NASA of the US in order to dissipate large amounts of heatgenerated in communication devices or electronic devices for artificialsatellites.

FIG. 2 is a schematic conceptual diagram of a conventional LHP system110. The conventional LHP system 110 includes a condenser 112, anevaporator 114, and a vapor line 116 and a liquid line 118 that connectthe condenser 112 and the evaporator 114 to one another to thereby forma loop.

FIG. 3 is a schematic conceptual diagram illustrating an operation ofthe LHP system 110 of FIG. 2.

The evaporator 114 includes a compensation chamber 112 that accommodatesa working fluid that is to be liquefied before permeating into asintered wick 120 included in the evaporator 114, to buffer the workingfluid. In the LHP system 110, the sintered wick 120 is installed only inthe evaporator 114, unlike the conventional straight heat pipe 100 (seeFIG. 1).

The LHP system 110 having the above-described structure operatesaccording to the following principle.

First, when a heating plate 124 of the evaporator 114 contacting a heatsource such as a heat generating component is heated, a working fluidpermeated into the sintered wick 120 is heated to a saturationtemperature by heat transmitted from the heating plate 124, and ischanged into a vapor.

The generated vapor is transferred to the condenser 112 along a vaporline 116 connected to a side of the evaporator 114. Next, as the vaporpasses through the condenser 112 and dissipates heat to the outside, thevapor is condensed, and the condensed working fluid is moved to theevaporator 114 again along a liquid line 118 connected to the condenser112, thereby repeating the above-described operation to cool the heatsource 101.

As illustrated in FIG. 3, the sintered wick 120 is bonded to an innercircumferential surface of the evaporator 114, and a space formed by theinner circumferential surface of the sintered wick 120 forms a vaporpassage through which the working fluid is changed into a vapor andmoves to the vapor line 116.

Meanwhile, the working fluid in a liquid state is changed into a vaporon a surface of the sintered wick 120. Accordingly, this surface isreferred to as an evaporation interface or a vapor-liquid interface.

The working fluid circulates while passing by points denoted by P1through P7. The working fluid is evaporated at the point P1, and theevaporated working fluid moves to the point P2 through the vapor pathinside the evaporator 114, and then moves to the point P3 along thevapor line 116. By passing from the points P3 and P4 at an inlet to thepoint P5 at an outlet of the condenser 112, the working fluid in a vaporstate is condensed again. The working fluid in a liquid state passes bythe point P6 at the inlet of the evaporator 114 along the liquid line118 and passes a compensation chamber 122 and is absorbed by thesintered wick 120 at the point P7 to move to the point P1 again.

In the LHP system 110, a force that causes movement of the working fluidis a capillary pumping force of the sintered wick 120. The capillarypumping force is related to a diameter of pores formed in the sinteredwick 120.

That is, if the diameter of pores formed in the sintered wick 120 isreduced, a capillary pumping force is increased. However, at the sametime, as the size of pores is reduced, flow resistivity of the sinteredwick 120 increases and thus permeability thereof decreases. Thus, it isdifficult to obtain desired cooling performance just by adjusting a sizeof pores in the sintered wick 120.

Consequently, a sintered wick included in an evaporator used in an LHPsystem needs to be configured such that a capillary pumping force isincreased but permeability is not decreased, so that a working fluid maybe effectively circulated.

SUMMARY OF THE INVENTION

The present invention provides an evaporator for a looped heat pipe(LHP) system, in which a capillary pressure is increased butpermeability is not decreased so as to facilitate circulation of aworking fluid inside the LHP system, thereby improving coolingefficiency for relatively long distance transportation and under arelatively high heat flux condition.

The present invention also provides a method of manufacturing theevaporator for an LHP system.

According to an aspect of the present invention, there is provided anevaporator for a looped heat pipe (LHP) system, in which a working fluidcirculates to cool a heat generating electronic component that generatesheat during operation, the evaporator including: a body comprising aninlet through which the working fluid enters and an outlet through whichthe working fluid is discharged; a sintered wick that is included in thebody, wherein the sintered wick is formed by sintering a copper powder,and a plurality of pores are formed in the sintered wick; and anadditional layer that is formed on a surface of the sintered wick,wherein the additional layer is formed by sintering copper particleshaving a size smaller than that of the copper powder forming thesintered wick, and the working fluid moved from the sintered wick ischanged in a vapor state to be discharged.

The thickness of the additional layer may be from 0.1 μm to 30 μm.

The thickness of the sintered wick may be from 1.0 mm to 2.0 mm.

By a hot pressing method in which heat and pressure are applied to theadditional layer, the additional layer may be sintered and may becombined with the sintered wick at the same time.

The sintered wick may be formed by sintering an irregular shaped microcopper powder having a size of 40 μm to 150 μm, and the additional layermay be formed by sintering sphere-shaped nano copper particles eachhaving a diameter of 10 nm to 200 nm.

According to another aspect of the present invention, there is provideda method of manufacturing an evaporator for a looped heat pipe (LHP)system, in which a working fluid circulates to cool a heat generatingelectronic component that generates heat during operation, the methodincluding: forming a body comprising an inlet through which the workingfluid enters and an outlet through which the working fluid isdischarged; forming a sintered wick that is included in the body,wherein the sintered wick is formed by sintering a copper powder, and aplurality of pores are formed in the sintered wick; and forming anadditional layer that is formed on a surface of the sintered wick,wherein the additional layer is formed by sintering copper particleshaving a size smaller than that of the copper powder forming thesintered wick, and the working fluid moved from the sintered wick ischanged in a vapor state to be discharged, wherein the forming of theadditional layer comprises: forming the additional layer by sinteringthe copper particles and combining the copper particles with thesintered wick at the same time by using a hot pressing method in whichheat and pressure are applied to the copper particles, in a state inwhich the copper particles are placed on the surface of the sinteredwick.

A pressure that is applied in the forming of the additional layer may befrom 10 Pa to 100 Pa, and a temperature during the forming of theadditional layer may be from 100° C. to 200° C.

A temperature during the forming of the additional layer may be from145° C. to 155° C.

Time during which the pressure and the heat are applied in the formingof the additional layer may be from 5 minutes to 15 minutes.

The thickness of the additional layer may be from 0.1 μm to 30 μm, andthe thickness of the sintered wick may be from 1.0 mm to 2.0 mm.

The copper powder forming the sintered wick may be an irregular shapedmicro copper powder having a size of 40 μm to 150 μm, and the copperparticles may be sphere-shaped nano copper particles each having adiameter of 10 nm to 200 nm.

The forming of the additional layer may be performed under air pressure.

The forming of the sintered wick may be performed for 3 to 7 hours, andthe forming of the additional layer may be performed for 5 to 15minutes.

The evaporator for an LHP system according to the embodiments of thepresent invention includes a thin additional layer consists of nanocopper particles that is formed on a vaporization surface of a sinteredwick formed of a micro-size copper powders by using a sintering bonding.Accordingly, the sintered wick coupled to the additional layer thatenhances capillary pressure while having minimal impact on permeability.

In addition, a contact thermal resistance between the additional layerand the vaporization surface of the sintered wick can be suppressed.Thus, a pressure loss of the sintered wick coupled to the additionallayer is decreased, and thus a working fluid inside the LHP system iscirculated smoothly with advanced capillary pressure generated by thesintered wick coupled to the additional layer. Thus, cooling efficiencyfor relatively long distance transportation and under a relatively highheat flux condition can be improved.

In addition, according to the method of manufacturing an evaporator foran LHP system, the additional layer formed of nano copper particles canbe easily formed on the vaporization surface of the sintered wick.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a schematic view illustrating an operation of a conventionalcylindrical heat pipe;

FIG. 2 is a conceptual diagram illustrating a conventional looped heatpipe (LHP) system;

FIG. 3 is a conceptual diagram for explaining an operation of theconventional LHP system of FIG. 2;

FIG. 4 is a conceptual diagram illustrating an LHP system in which anevaporator according to an embodiment of the present invention isincluded;

FIG. 5 is a partial perspective view of the evaporator of FIG. 4according to an embodiment of the present invention;

FIG. 6 is a conceptual cross-sectional view in which a body, a sinteredwick, and a portion of an additional layer, which is illustrated in FIG.5, are magnified;

FIGS. 7 and 8 are photographic images of cross sections of the sinteredwick and additional layer illustrated in FIG. 5, photographed using ascanning electronic microscope (SEM); and

FIGS. 9 through 11 are conceptual diagrams for explaining a method ofmanufacturing an evaporator for an LHP system according to an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an evaporator that is one of variouselements of a looped heat pipe (LHP) system.

FIG. 4 is a conceptual diagram illustrating an LHP system 110 in whichan evaporator according to an embodiment of the present invention isincluded.

Referring to FIG. 4, the LHP system 110 includes an evaporator 1according to an embodiment of the present invention, a condenser 112, avapor transport line 116, and a liquid transport line 118.

The condenser 112 changes a working fluid in a vapor state andtransmitted from the evaporator 1 into a liquid. The condenser 112 takesheat from the working fluid to dissipate the heat to outer air.

Also, the vapor transport line 116 is a line member that connects theevaporator 1 and the condenser 112 so that the working fluid changedinto a vapor state in the evaporator 1 may be transported to thecondenser 112. The liquid transport line 118 is a line member thatconnects the condenser 112 and the evaporator 1 so that the workingfluid changed into a liquid state in the condenser 112 may be suppliedto the evaporator 1 again.

Meanwhile, the general description and operations as described in therelated art of the invention apply to the condenser 112, the vaportransport line 116, and the liquid transport line 118.

Hereinafter, the evaporator 1 for an LHP system according to the currentembodiment of the present invention will be described in detail withreference to FIGS. 4 through 8.

FIG. 4 is a conceptual diagram illustrating the LHP system 110 in whichthe evaporator 1 according to the current embodiment of the presentinvention is included. FIG. 5 is a partial perspective view of theevaporator 1 of FIG. 4. FIG. 6 is a conceptual cross-sectional viewillustrating a body 10, a sintered wick 20, and an additional layer 30,which are included in the evaporator 1 of FIG. 5. FIGS. 7 and 8 arephotographic images of the sintered wick 20 and additional layer 30captured using a scanning electronic microscope (SEM).

The evaporator 1 for an LHP system according to the current embodimentof the present invention includes the body 10, the sintered wick 20, andthe additional layer 30.

The body 10 is in contact with a heat generating electronic component(not shown) to receive heat generated during operation of the heatgenerating electronic component (see “heat” and arrows indicating thesame shown in FIG. 4). The body 10 is formed of copper having arelatively high thermal conductivity.

In the current embodiment, the body 10 has a shape in which a hexahedronopened in one direction is formed in a body and a separately formedmember is coupled to an open surface of the hexahedron. However, inother embodiments, the body 10 may be variously modified such that alower surface thereof is formed of a separate member and is coupled toother members.

Meanwhile, the body 10 is formed to contact a heat generating componentat a portion of an outer surface of the body 10. That is, the body 10can receive heat when the heat generating component contacts a portionof an outer lower surface or lateral surface of the body 10.

Inside the body 10, a compensation chamber 16 and the sintered wick 20including the additional layer 30 are formed. An inlet 12 and an outlet14 are formed in the body 10. The inlet 12 and the outlet 14 areconceptually illustrated in FIG. 5. According to the current embodiment,the compensation chamber 16 is formed at the inlet 12 of the body 10.

A working fluid that circulates through the LHP system 110 flows intothe body 10 in a liquid state through the inlet 12. The working fluid ina liquid state is contained in the compensation chamber 16 before movingto the sintered wick 20. Through the outlet 14, the working fluid in avapor state is discharged out of the body 10. That is, the working fluidis changed into a vapor by passing through the sintered wick 20 and theadditional layer 30, and is discharged out of the body 10 after passinga vapor removal space 18 surrounded by the additional layer 30. Thedischarged working fluid is moved to the condenser 112 via the vaportransport line 116.

The sintered wick 20 is contained in the body 10. The sintered wick 20is formed by sintering a copper powder. The sintered wick 20 is a porousmaterial in which a large number of pores are formed.

Meanwhile, according to the current embodiment of the present invention,the thickness of the sintered wick 20 is in the range of from 1.0 mm to2.0 mm. The sintered wick 20 is formed by sintering an irregular shapedmicro copper powder having a size of 40 μm to 150 μm.

The pores formed in the sintered wick 20 may be formed using a generalmethod of forming a sintered wick using a copper powder, and such that adiameter of the pores is in a range from about 100 to about 200 μm.

As the working fluid in a liquid state flows into the sintered wick 20,the pores having a diameter in the above-described range suppress theflow resistivity of the working fluid and thus allow good permeabilityof the working fluid. However, the pore size may be adjusted accordingto the type of working fluid used in the LHP system 200, the length of atransport line, and a cooling range.

The specific shape of the sintered wick 20 may be modified variously aslong as the working fluid flown through the inlet 12 satisfies apredetermined condition of being discharged from the outlet 14 afterpassing the sintered wick 20. That is, in the current embodiment, thesintered wick 20 is made in one body as a shape of a hexahedron openedin one direction. However, according to some embodiments, the sinteredwick 20 may be made in a plate shape.

The additional layer 30 is included in the sintered wick 20 as if coatedon the sintered wick 20. In the additional layer 30, the working fluiddelivered from the sintered wick 20 is changed in a vapor state and isdischarged to the outside of the additional layer 30.

The additional layer 30, like the sintered wick 20, is formed of acopper material. Since both the sintered wick 20 and the additionallayer 30 are formed of the copper material, contact thermal resistanceat an interface therebetween is lowered.

The additional layer 30 is formed by sintering copper particles having asize smaller than that of the copper powder forming the sintered wick20.

In the current embodiment, the additional layer 30 is formed bysintering sphere-shaped nano copper particles each having a diameter of10 nm to 200 nm. Since the additional layer 30 is formed by sinteringthe nano copper particles each having the diameter of 10 nm to 200 nm, aplurality of pores formed therein also have a nano size corresponding tothe size of the nano copper particles.

In the current embodiment, the thickness of the additional layer 30 isin a range of from 0.1 μm to 30 μm. If the thickness of the additionallayer 30 is less than the thickness in the range, it is difficult toactually form the additional layer 30. If the thickness of theadditional layer 30 is greater than the thickness in the range,permeability of the working fluid deteriorates due to flow resistance ofthe working fluid and thus a pressure loss increases. Accordingly, totalpressure drop of the LHP system 110 is lowered so that a heat transferperformance of the LHP system 110 may be higher.

If the shape of the sintered wick 20 is modified, a detailed shape ofthe additional layer 30 is also modified to correspond to themodification of the shape of the sintered wick 20.

In the current embodiment, by a hot pressing method in which copperparticles are heaped on the sintered wick 20 and heat and pressure areapplied thereto, the additional layer 30 is sintered and is combinedwith the sintered wick 20 at the same time to become one body with thesintered wick 20.

However, in another embodiment, after separately forming an additionallayer, this additional layer may be combined with the sintered wick 20by the hot pressing method. In this case, contact thermal resistance ishigher compared to the current embodiment, and thus, a vapor temperatureincreases, thereby increasing an operating temperature of the LHP system110. Thus, there is a disadvantage that a system thermal resistanceincreases, but effects other than the disadvantage may be obtained.

FIG. 7 is a photographic image of a cross section of the sintered wick20 and additional layer 30, photographed using a scanning electronicmicroscope (SEM), and FIG. 8 is a photographic image in which a crosssectional portion of the additional layer 30 is magnified. Referring tothe photographic images of FIGS. 7 and 8, micro pores are formed in thesintered wick 20, and nano pores are formed in the additional layer 30.

Hereinafter, function and effects of the evaporator 1 of the LHP system200 having the above-described structure will be described in detail.

An operation of the LHP system 110 including the evaporator 1 accordingto the current embodiment of the present invention will be brieflydescribed with reference to FIG. 4.

A surface of the body 10 of the evaporator 1 is contacted to a heatgenerating electronic component (not shown). Heat generated by the heatgenerating electronic component is transmitted to the sintered wick 20included in the body 10, and the heat is transmitted to the additionallayer 30 disposed on a surface of the sintered wick 20. The liquid phaseof the working fluid is changed into a vapor phase by the transferredheat and then is discharged from the additional layer 30.

The working fluid changed into a vapor state is discharged to theoutside of the evaporator 1 through the outlet 14. The dischargedworking fluid is moved to the condenser 112 to be changed into a liquidstate as heat is taken away from the working fluid, and then the workingfluid flows along the liquid transport line 118 and through the inlet 12of the body 10 and into the compensation chamber 16 of the body 10.

The working fluid in a liquid state flown into the compensation chamber16 permeates between the pores of the sintered wick 20 due to acapillary pumping force due to the pores of the sintered wick 20. Theworking fluid in a liquid state and permeated between the pores of thesintered wick 20 permeates between the pores of the additional layer 30by a capillary pumping force of the additional layer 30 again. Theworking fluid permeated between the pores is heated by sensible heat,which is transferred from the heat generating electronic component, andthus is changed into a vapor state, and moves to the space 18 afterbeing changed to latent heat. The working fluid circulates in this way,thereby cooling the heat generating electronic component.

Here, a capillary pumping force, which is generally referred to as“capillary pressure”, is given by the following equation.

$P = \frac{2\sigma}{r}$

P denotes a capillary pressure, σ denotes a surface tension of theworking fluid, and r denotes an effective radius of the pores of thesintered wick 20 sintered by metal particles such as copper andaluminum. Since the surface tension of the working fluid is constant, acapillary pumping force is inversely proportional to the effectiveradius of the pores of the sintered wick 20 sintered by metal particlessuch as copper, and nickel. That is, the smaller the effective radius ofthe pores, the greater the capillary pumping force.

Meanwhile, permeability of the working fluid is proportional to theeffective radius of the pores. That is, the smaller the effective radiusof the pores, the smaller the permeability.

Like general sintered wicks, the sintered wick 20 according to thecurrent embodiment of the present invention also has micro-scale pores,and the additional layer 30 including a plurality of nano-scale pores isformed on the surface of the sintered wick 20 so as to improve acapillary pumping force while to have the minimal impact of permeabilityof the working fluid. Consequently, the working fluid may be easilycirculated, thereby improving cooling performance.

That is, the working fluid in a liquid state may have no difficulty inpassing through the sintered wick 20 in which micro-scale pores areformed. In addition, due to the nano-scale pores formed in theadditional layer 30, a capillary pumping force is more strengthened,thereby facilitating circulation of the working fluid.

In other words, the evaporator 1 for an LHP system according to thecurrent embodiment of the present invention includes the additionallayer 30 including nano-scale pores, which is formed on the surface ofthe sintered wick 20, and thus, a capillary pumping force is improvedand permeability of the working fluid through the sintered wick 20 isnot lowered.

That is, by disposing the additional layer 20 formed by sintering ofnano-scale copper particles on the sintered wick 20 formed by sinteringof micro-scale copper powder, influence on the permeability of theworking fluid is minimized and a high capillary pumping force isprovided, and thus, cooling performance may be strengthened. Inaddition, this configuration may maintain the same feat flux and maycompensate for a geometrical limitation.

Hereinafter, a method of manufacturing an evaporator for an LHP systemaccording to an embodiment of the present invention will be described.

According to the method of manufacturing an evaporator for an LHP systemaccording to the current embodiment of the present invention, anevaporator that is an element of an LHP system, in which a working fluidcirculates to cool a heat generating component heated during operation,is manufactured.

The method of manufacturing an evaporator for an LHP system according tothe current embodiment of the present invention will be described withreference to FIGS. 9 through 11 below. FIG. 9 is a diagram form forexplaining a process of forming a sintered wick (step 1), and FIG. 10 isa diagram form for explaining a process of forming an additional layer(step 2), and FIG. 11 is a time-temperature graph concerning the processof forming a sintered wick and the process of forming an additionallayer.

An evaporator 1 manufactured by the method of manufacturing anevaporator according to the current embodiment of the present inventionincludes a body 10, a sintered wick 20, and an additional layer 30.Elements of the evaporator 1 are identical or similar to those of theevaporator 1 described above, and thus description thereof will not berepeated, and previous description or appropriate modification of thedescription will apply.

One of major features of the method of manufacturing an evaporatoraccording to the current embodiment of the present invention is relatedto how the additional layer 30 is disposed on the sintered wick 20.Hereinafter, configurations related to the additional layer 30 will bemainly described.

Although the sintered wick 20 included in the evaporator 1 describedabove has a shape of a hexahedron having an opened one side and includesthe additional layer 30 formed at the sintered wick 20, in the followingdescription of the method of manufacturing an evaporator, a case inwhich a sintered wick having a plate form is formed and an additionallayer is further disposed on the upper side of the sintered wick isexplained as an example to conceptually explain the method.

The shape of the hexahedron having an opened one side may bemanufactured by a mold having a shape corresponding to the hexahedralshape. For example, a sintered wick, which has a shape of a hexahedronhaving an opened one side, and an additional layer, which is disposed onthe surface of the sintered wick, may be formed by an external moldhaving an opened one side and an internal mold that is disposed insidethe external mold and is located spaced apart from the external mold bya predetermined interval.

The additional layer 30 disposed on the sintered wick 20 is manufacturedby a process including a process of forming a sintered wick and aprocess of forming an additional layer.

The process of forming a sintered wick is a process of forming asintered wick by heating copper powder. Referring to FIG. 9, copperpowder 20′ is put in a usual isothermal furnace and then is sintered byheating the copper powder.

The copper powder 20′ is micro copper powder having an irregular shapeand a size of 40 μm to 150 μm. The reference numeral 20′ denotes copperpowder before the sintered wick 20 is formed.

The sintered wick 20 is manufactured so that the thickness thereof is inrange of 1.0 mm to 2.0 mm. In this case, to obtain a sintered wickhaving a desired thickness, the amount of necessary copper powder isadjusted by calculating a necessary weight in consideration of thethickness and length of the sintered wick to be manufactured and thedensity of the copper.

In the process of forming a sintered wick, a preferable heatingtemperature may be in a range of 500° C. to 700° C., and the mostpreferable heating temperature is about 600° C. Referring to FIG. 11,the extent of heating and the extent of cooling are shown in the processof forming a sintered wick (step 1). The process of forming a sinteredwick is performed for 3 to 7 hours.

Referring to FIG. 9, the inside of the isothermal furnace maintains avacuum state, thereby suppressing oxidation of the copper powder. Inaddition, the isothermal furnace includes a heating apparatus and acooling apparatus, and thus may adjust a temperature of the inside ofthe isothermal furnace.

Next, the process of forming an additional layer (step 2) is performed.The process of forming an additional layer (step 2) is a process offorming an additional layer on the sintered wick 20 formed through thepreceding process.

In the process of forming an additional layer (step 2), copper particlessmaller than the copper powder used when forming the sintered wick 20are used to manufacture an additional layer. Referring to FIG. 10,pressure and heat are applied in a state in which copper particles 30′are placed on the surface of the sintered wick 20. That is, by using thehot pressing method, the copper particles 30′ are sintered and arecombined with the surface of the sintered wick 20 at the same time.

In the current embodiment, a pressure that is applied in the process offorming the additional layer is from 10 Pa to 100 Pa, and a temperaturethat is applied in the process of forming the additional layer is from100° C. to 200° C. The most suitable heating temperature is about 150°C. In addition, time during which the pressure and the temperature areapplied is from 5 minutes to 15 minutes. The pressure, the temperature,and the time are appropriately determined in consideration of thethickness of the additional layer to be manufactured, the size of thecopper particles 30′, and the size of pores.

In the current embodiment, the thickness of the additional layer is from0.1 μm to 30 μm. Referring to FIG. 10, the copper particles 30′ that areplaced on the surface of the sintered wick 20 are sphere-shaped nanocopper particles having a diameter of 10 nm to 200 nm. The referencenumeral 30′ denotes the copper particles that become the additionallayer after sintering.

Referring to FIG. 10, a vacuum pump, a unit for applying pressure, aheating unit, and a cooling unit are provided to perform the process offorming an additional layer (step 2).

Although in the current embodiment, the process of forming an additionallayer is performed in a vacuum state, the present invention is notlimited thereto. That is, in another embodiment, the process of formingan additional layer may be performed in an air pressure state.

Consequently, a sintered wick including an additional layer may bemanufactured via the process of forming a sintered wick (step 1) and theprocess of forming an additional layer (step 2), and an evaporatorincluding the sintered wick including the additional layer may bemanufactured. By using the evaporator in an LHP system, a capillarypumping force of sintered wick 20 may be increased but permeability ofsintered wick 20 may not decrease, thereby improving coolingperformance.

According to the method of manufacturing an evaporator for an LHPsystem, the additional layer having nano pores may be formed on thesintered wick having micro pores. In addition, at the same time assintering the additional layer, the additional layer may be combinedwith the sintered wick 20. The evaporator manufactured according to themethod may obtain the above stated advantages.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. An evaporator for a looped heat pipe (LHP)system, in which a working fluid circulates to cool a heat generatingelectronic component that generates heat during operation, theevaporator comprising: a body comprising an inlet through which theworking fluid enters and an outlet through which the working fluid isdischarged; a sintered wick that is included in the body, wherein thesintered wick is formed by sintering a copper powder, and a plurality ofpores are formed in the sintered wick; and an additional layer that isformed on a surface of the sintered wick, wherein the additional layeris formed by sintering copper particles having a size smaller than thatof the copper powder forming the sintered wick, and the working fluidmoved from the sintered wick is changed in a vapor state to bedischarged.
 2. The evaporator for an LHP system of claim 1, wherein thethickness of the additional layer is from 0.1 μm to 30 μm.
 3. Theevaporator for an LHP system of claim 1, wherein the thickness of thesintered wick is from 1.0 mm to 2.0 mm.
 4. The evaporator for an LHPsystem of claim 1, wherein by a hot pressing method in which heat andpressure are applied to the additional layer, the additional layer issintered and is combined with the sintered wick at the same time.
 5. Theevaporator for an LHP system of claim 1, wherein the sintered wick isformed by sintering an irregular shaped micro copper powder having asize of 40 μm to 150 μm and the additional layer is formed by sinteringsphere-shaped nano copper particles each having a diameter of 10 nm to200 nm.
 6. A method of manufacturing an evaporator for a looped heatpipe (LHP) system, in which a working fluid circulates to cool a heatgenerating electronic component that generates heat during operation,the method comprising: forming a body comprising an inlet through whichthe working fluid enters and an outlet through which the working fluidis discharged; forming a sintered wick that is included in the body,wherein the sintered wick is formed by sintering a copper powder, and aplurality of pores are formed in the sintered wick; and forming anadditional layer that is formed on a surface of the sintered wick,wherein the additional layer is formed by sintering copper particleshaving a size smaller than that of the copper powder forming thesintered wick, and the working fluid moved from the sintered wick ischanged in a vapor state to be discharged, wherein the forming of theadditional layer comprises: forming the additional layer by sinteringthe copper particles and combining the copper particles with thesintered wick at the same time by using a hot pressing method in whichheat and pressure are applied to the copper particles, in a state inwhich the copper particles are placed on the surface of the sinteredwick.
 7. The method of claim 6, wherein a pressure that is applied inthe forming of the additional layer is from 10 Pa to 100 Pa, and atemperature during the forming of the additional layer is from 100° C.to 200° C.
 8. The method of claim 6, wherein a temperature during theforming of the additional layer is from 145° C. to 155° C.
 9. The methodof claim 6, wherein time during which the pressure and the heat areapplied in the forming of the additional layer is from 5 minutes to 15minutes.
 10. The method of claim 6, wherein the thickness of theadditional layer is from 0.1 μm to 30 μm, and the thickness of thesintered wick is from 1.0 mm to 2.0 mm.
 11. The method of claim 6,wherein the copper powder forming the sintered wick is an irregularshaped micro copper powder having a size of 40 μm to 150 μm, and thecopper particles are sphere-shaped nano copper particles each having adiameter of 10 nm to 200 nm.
 12. The method of claim 6, wherein theforming of the additional layer is performed under air pressure.
 13. Themethod of claim 6, wherein the forming of the sintered wick is performedfor 3 to 7 hours, and the forming of the additional layer is performedfor 5 to 15 minutes.